Interrogations-and-Confessions-Handbook

Persons at Risk During Interviews in Police Custody 63
Table 3.2. The mean and standard deviation
scores from the psychological tests
Test Mean S.D.
IQ test:
Full Scale IQ 82 14
Verbal IQ 83 14
Performance IQ 83 19
Reading test:
Raw score 74 20
Suggestibility test:
Immediate Recall 11.6 6.4
Delayed Recall 10.5 6.4
Yield 5.6 3.7
Shift 4.3 3.5
Total Suggestibility 10.0 6.0
Anxiety test:
Trait Anxiety 42.9 12.0
State Anxiety 53.6 13.5
From Gudjonsson et al., 1993.
mean of 83, which is over one standard deviation below the mean of 100 for the
general adult population. In fact, the mean scores fall at the bottom 15% of the
general population. There was a wide range of scores, with prorated Full Scale
IQ ranging from 61 to 131. Fourteen (9%) of the total sample had a Full Scale IQ
below 70 (i.e. bottom 2% of the general population); about a third (34%) had an
IQ of 75 or below (i.e. bottom 5% of the general population). Sixty-eight (42%)
subjects had a Full Scale IQ that fell in the ‘borderline’ range (i.e. IQ between
70 and 79). The results indicate that a large number of detainees suffer from
a significant intellectual impairment or fall in the borderline range of ‘mental
handicap’.
The mean score obtained on the Schonell Graded Word Reading Test was 74.
This gives an average reading age of 11 years and 8 months. The scores extended
across the full range, 0 to 100. Eleven (7%) of the detainees obtained a score
below 43, which represents a reading age of below nine years and functional
illiteracy.
In the study, reading ability correlated only modestly with prorated Verbal
Scale IQ (r = 0.40, p < 0.001) and not at all significantly with prorated Performance
IQ (r = 0.16, ns). In addition, only five (45%) of the 11 detainees with
a reading age below nine years had a prorated Full Scale IQ of below 75 and
only one (9%) below 70. Conversely, nine of the subjects with a reading age
above nine years had a prorated Full Scale IQ of below 70. The findings suggest
that reading ability is not a good indicator of an intellectual deficit. Reading
ability is not a direct function of intellectual ability, although they are modestly
correlated.
The immediate and delayed memory scores obtained on the GSS 2 are well
below those found for the normal population, but they are consistent with the